A magazine is an ammunition storage and feeding device within, or attached to, a repeating firearm. The magazine functions by moving the cartridges stored in the magazine into a position where they may be chambered by the action of the firearm. Most magazines designed for use with a reciprocating bolt firearm utilize a set of feed lips which stops the vertical motion of the cartridges out of the magazine but allows one cartridge at a time to be pushed forward (stripped) out of the feed lips by the firearm's bolt into the chamber.
Some form of spring and follower combination is almost always used to feed cartridges to the lips, which can be located either in the magazine (most removable box magazines) or built into the firearm (fixed box magazines). A box (or “stick”) magazine, the most popular type of magazine in modern rifles and handguns, stores cartridges in a straight or gently curved column, either one above the other or staggered zigzag fashion. As the firearm cycles, cartridges are moved to the top of the magazine by a follower driven by spring compression to either a single feed position or alternating feed positions. In most firearms, the magazine follower engages a slide-stop to hold the slide back and keep the firearm out of battery when the magazine is empty and all rounds have been fired. Box magazines may be integral to the firearm or removable.
A detachable box magazine is a self-contained mechanism capable of being loaded or unloaded while detached from the host firearm. They are inserted into a magazine well in the firearm receiver usually below the action, but occasionally positioned to the side or on top. When the magazine is empty, it can be detached from the firearm and replaced by another full magazine while the firearm remains in an operable state. This significantly speeds the process of reloading, allowing the operator quick access to ammunition. This type of magazine may be straight or curved, the curve being necessary if the rifle uses rimmed ammunition or ammunition with a tapered case.
In some jurisdictions, a semi-automatic firearm such as the extremely popular AR-15 rifle, is prohibited to the general public when it is equipped with a conventional detachable box magazine that enables rapid reloading. However, if the semi-automatic firearm is equipped with a fixed magazine that cannot be removed from the firearm unless the firearm is in an inoperable state, the firearm is not prohibited, and is not subject to the associated legal restrictions.
People seeking to develop skills and enjoy the many advances of the AR-15 platform, but who live in jurisdictions where standard versions are prohibited, require a fixed magazine version of the rifle. However, this requires the rifle design to deviate substantially from the conventional format. Moreover, there are challenges with loading a fixed magazine on an AR-15 rifle, including access to the open end of the magazine, and time to load each cartridge. In addition, people prefer to own a rifle that can be adapted to conventional use with detachable magazines in the event the owner leaves the jurisdiction where the prohibition applies. Thus, existing rifles that comply with prohibitions are less desirable when they have configurations or modifications that render them unable to accept conventional detachable magazines.
Therefore, a need exists for a new and improved takedown pin for a rifle that enables a semi-automatic firearm to be opened and closed without requiring complete removal of the takedown pin. In this regard, the various embodiments of the present invention substantially fulfill at least some of these needs. In this respect, the takedown pin for a rifle according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of providing a semi-automatic firearm that can be opened and closed without requiring complete removal of the takedown pin.